1. Field of the Invention
The present invention relates to a magnetic separator which continuously concentrates magnetic materials from a gas or liquid which contains a mixture of magnetic materials or magnetic and non magnetic materials.
2. Prior Art
Many previously patented magnetic separators have been designed to remove impurities from an ore slurry or a process fluid or a food process or to remove a useful mineral or compound or element which is more valuable if concentrated. Those separators are either of the intermittent type, which must be periodically flushed, or the continuous type.
Three types of magnetic materials are ferromagnetic, paramagnetic and diamagnetic. Ferromagnetic materials have large positive susceptibilities. Paramagnetic materials have susceptibilities which are slightly positive and diamagnetic materials have slightly negative susceptibilities. A vacuum has zero susceptibility.
The magnitude of the force which can be exerted on a magnetic material is dependent upon a) its induced magnetization, which is proportional to its magnetic susceptibility and the magnetic field, b) the gradient of the magnetic field or the change in magnetic field strength with respect to position in the magnetic field, and c) magnetic material size.
Because magnetic susceptibilities vary from thousands of e m u (electromagnetic units) positive for ferromagnetic materials to slightly positive for paramagnetic materials and slightly negative for diamagnetic materials, the forces which can be exerted vary greatly. Therefore prior art designs vary depending upon the magnetic material to be separated.
The most difficult magnetic materials to separate are the paramagnetic and diamagnetic materials, because the forces are much smaller than with ferromagnetic materials for a given magnetic field.
Prior art designs to separate paramagnetic and diamagnetic materials have increased the magnetic field strength and the magnetic field gradient to increase the forces on those materials. The Kolm-type separator, see U.S. Pat. No. 3,676,337, employs a fibrous matrix of ferromagnetic wool placed in a high d.c. magnetic field. The random orientation of the fibers and the high magnetic field saturates the ferromagnetic fibers and certain regions within the matrix produce very high magnetic gradients. Those regions of high magnetic gradients are produced randomly throughout the matrix. The material to be separated is passed through the fiber matrix and the paramagnetic materials are attracted to the high gradient areas and embed themselves in those areas. Eventually the magnetic field must be turned off and the matrix flushed to remove the paramagnetic materials.
To overcome the requirement of periodically flushing the matrix, several continuous operation magnetic separators have been proposed.
Kelland in U.S. Pat. No. 4,261,815 discloses a separator apparatus in which a grid of fine ferromagnetic wires are arranged parallel to the flow of the fluid to be separated and a strong magnetic field is produced perpendicular to the wires and the flow. The wires distort the magnetic field and result in a magnetic gradient around the wires which concentrates magnetic materials on opposite sides along each wires axis. As the wires near the end of the magnetic field there is a grid matrix for separation of the flows from each wire. This results in the need for small openings for each wire, which can become clogged and are difficult to fabricate.
Vollmar in U.S. Pat. No. 4,816,143 discloses a method and apparatus for continuous separation of paramagnetic and/or diamagnetic particles from a flowing fluid by guiding the fluid through a multiplicity of openings which subject the fluid to a magnetic gradient produced by ferromagnetic pole element orifices. Separation is achieved when the magnetic materials of different susceptibilities flow into the opening in the orifice or away from the opening. Means are provided to deliver the fluid to the openings, and to separate the flows of the materials with different susceptibilities. There are a multiplicity of openings and orifices in a separation canister but the fluid passes through a feed opening only once in each canister and is then diverted to either the higher or lower susceptibility outlet. In order to achieve higher separations the canisters must be cascaded, with each outlet flow becoming a homogeneous mixture because of the natural mixing which takes place as the fluids travel through the channels or piping between separation orifices.